Dr Mahathir said he was confident that prosecutors will be able to build up a strong case to bring charges against the former leader over graft claims linked to 1Malaysia Development Bhd (1MDB).

"We are slowly getting to the bottom of things and many of our senior officers are volunteering information accompanied, of course, by documents.

"We think that within a short while we will have a case against him, we will be able to charge him," he said via video conference to The Wall Street Journal CEO Council Meeting in Tokyo.

Dr Mahathir added that he was facing the problem of "trying to trust people to investigate him".

"Some of these people who were with him had sided with him and we do not know who is going to be loyal to this new government," he said.

When asked if he might be willing to cut a deal to spare Najib, if he were to offer information that can recover part of the US$4.5bil (RM18.19bil) allegedly lost by 1MDB, Dr Mahathir would only say: "No deal".

Dr Mahathir had personally ordered travel restrictions on Najib last Saturday (May 12) after news spread that the latter was about to fly off to Jakarta for a short break.

He also told the conference that he will remain as Prime Minister for one or two years – and would continue to play a role in the background even after he steps down.

Meanwhile, former Inspector-General of Police Tan Sri Khalid Abu Bakar has been added to the list of those banned from travelling abroad.

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